Implementing Memorize

[Lutz Donnerhacke <lutz@iks-jena.de>]

In order to implement a generic memorize, I tried the following
  (see <slrnbpajhj.ns.lutz@taranis.iks-jena.de> for the context)

   generic
      with function Callback (n : Natural) return Natural;
   function Action (n : Natural) return Natural;
   
   function Action (n : Natural) return Natural is
   begin
      case n is
         when 0 | 1  => return 1;
         when others => return Callback(n-1) + Callback(n-2);
      end case;
   end Action;
   
   function Fib_Direct is new Action (Fib_Direct); -- won't compile